FIG. 1 is a schematic view illustrating a printing unit of a thermal transfer printer apparatus 1.
During printing, a thermal head 2 and a platen roller 3 are pressed against each other with a recording sheet 4 and an ink sheet 5 therebetween. A plurality of heating elements linearly arranged along the length of the thermal head 2 generate heat and thereby transfer ink on the ink sheet 5 onto the recording sheet 4, which, in turn, is conveyed by a recording sheet conveying mechanism that is positioned downstream of the conveying direction during printing, and the ink sheet 5 is conveyed by an ink sheet take-up mechanism. In synchronization with the conveyance of the recording sheet 4 and the ink sheet 5, the plurality of heating elements selectively generate heat to form an image. After ink is transferred, the recording sheet 4 and the ink sheet 5 are conveyed by their respective conveying mechanisms to the downstream of their conveying paths, which diverge in the middle. The recording sheet 4 is directed to a paper ejecting portion, and the ink sheet 5 is separated from the recording sheet 4 by a separating member 6 and taken up by a take-up bobbin 12. The separating member 6 is positioned near a diverging point at which the conveying paths diverge.
FIG. 2 is a perspective view illustrating a state wherein an ink ribbon cassette 7, into which the ink sheet 5 is stored, is inserted into, or removed from, a main body of the printer apparatus 1.
In a thermal transfer printer, such as the printer apparatus 1, the ink ribbon cassette 7 is inserted into, and removed from, the printer apparatus 1 along the length of the thermal head 2, through an opening 1a that is provided on one side of the main body of the printer apparatus 1. During insertion and removal of the ink ribbon cassette 7, the ink sheet 5 passes through a space between the thermal head 2 and the platen roller 3.
FIG. 3 illustrates a typical conventional printer with the above-described configuration. When an ink ribbon cassette 7 is inserted into, and removed from, a main body of a printer apparatus 1, a thermal head 2 is fully retracted from a platen roller 3, as illustrated. Given that doing so provides sufficient clearance between the thermal head 2 and the platen roller 3, an ink sheet 5 is prevented from coming into contact with the thermal head 2 or the platen roller 3. Jamming of the ink sheet 5 is thus prevented.
FIG. 4 illustrates another type of a conventional printer, such as that disclosed in Japanese Patent Laid-Open No. 08-112951. A printer apparatus 1 in FIG. 4 is configured such that a thermal head 2 is secured to a main body of the printer apparatus 1, and that a platen roller 3 is moved when an ink ribbon cassette 7 is inserted into, or removed from, the main body of the printer apparatus 1. Given that the platen roller 3 is retracted from the thermal head 2, sufficient clearance is provided between the thermal head 2 and the platen roller 3. Jamming of an ink sheet 5 is thus prevented.
Examples of methods for securing a thermal head to a printer main body include a method in which a thermal head is fixed as a cantilever. That is, in this method, the thermal head is supported at one end and left free at the other end. FIG. 5 is a cross-sectional view illustrating a printing mechanism of a printer apparatus 1 in which a thermal head 2 is secured to a main body of the printer apparatus 1 as a cantilever. Referring to FIG. 5, an opening 1a for insertion of an ink ribbon cassette (not shown) is provided on one side of the printer apparatus 1. During insertion and removal of the ink ribbon cassette, an ink sheet (not shown) passes through a space between the thermal head 2 and the opening 1a. During printing, a free end of the thermal head 2 is secured to a surface of a lid (not shown) for the opening 1a, the surface being adjacent to the printer apparatus 1. The lid for the opening 1a is provided with a hole, into which a supporting member 2a for the thermal head 2 is to be fitted. The supporting member 2a not only enables accurate positioning of the thermal head 2, but also supports the free end of the thermal head 2. Therefore, the thermal head 2 is fixed at both ends, like a simple beam, and can withstand contact pressure of a platen roller 3 during printing.
There is another printer in which a thermal head and a separating member, such as the separating member 6 of FIG. 1, are covered with a guiding member, such as that indicated by reference numeral 8 in FIG. 5, so that an ink sheet comes into contact with the guiding member, and is introduced into the printer without causing jamming. There is still another printer in which, to reduce the possibility of jamming, a separating member and a guiding member are integrally molded of resin material, so that these members are seamlessly joined together.
However, if the printer apparatus 1 is configured such that the thermal head 2 is moved, as illustrated in FIG. 3, it is necessary to allow space for the thermal head 2 to retract. Moreover, since the thermal head 2 moves back and forth between the retracting position and the printing position, it is necessary to control the position of the thermal head 2 with high precision when the thermal head 2 is at the printing position, so as not to affect printing performance. It is thus required to ensure positioning accuracy.
If the printer apparatus 1 is configured such that the platen roller 3 is moved, as illustrated in FIG. 4, there is no need for the thermal head 2 to retract. Therefore, once the thermal head 2 is secured to the main body of the printer apparatus 1 and the required mounting accuracy is achieved, the printing position of the thermal head 2 can be automatically set.
However, the above-described configuration, where the thermal head 2 is fixed, may cause other problems.
In the typical thermal transfer printer apparatus 1 illustrated in FIG. 1, the ink sheet 5 is conveyed along the conveying path, while being pulled toward the thermal head 2. In the printer apparatus 1 where the thermal head 2 retracts, as illustrated in FIG. 3, the thermal head 2 moves to a retracting position, which provides sufficient clearance between the thermal head 2 and the ink sheet 5. Therefore, when the ink ribbon cassette 7 is inserted into the main body of the printer apparatus 1, the ink sheet 5 can be prevented from coming into contact with the thermal head 2.
However, in the printer apparatus 1 where the platen roller 3 retracts, as illustrated in FIG. 4, the thermal head 2 is secured to the main body of the printer apparatus 1. Therefore, during insertion and removal of the ink ribbon cassette 7, the ink sheet 5 tends to come into contact with an end portion of the thermal head 2 or the separating member 6, thus causing jamming to occur.
It is possible to prevent jamming of the ink sheet by providing the guiding member 8, as illustrated in FIG. 5. However, since the ink sheet comes into contact with the guiding member 8 in this case, the surface of the ink sheet may be scratched, and printing quality may be affected.
Moreover, since the thermal head 2 of FIG. 5 is fixed as a cantilever, the ink ribbon cassette comes into contact with the thermal head 2 during insertion and removal, and thus causes the thermal head 2 to bend. This narrows the clearance between the thermal head 2 and the opening 1a for allowing the ink sheet to pass therethrough, and prevents smooth passage of the ink sheet, thus causing jamming to occur.